1. Field of the Invention
The present invention relates to a method of manufacturing a single crystal of compound semiconductor in accordance with vertical solidification and an apparatus for the same.
2. Description of the Related Art
Conventional methods of manufacturing a single crystal of compound semiconductor in accordance with vertical solidification employ a gradual cooling technique with a vertical temperature gradient (Journal of Crystal Growth 74 (1986) 491-506). In this method, a compound semiconductor polycrystal synthesized in advance is used as a raw material and placed in a crucible and melted. The obtained melt is caused to contact with a seed crystal arranged in the bottom of the crucible, thereby performing seeding. The crucible is gradually cooled from its lower to upper portion to grow a single crystal of compound semiconductor.
In this method, a Group V element is arranged in the lower low-temperature portion of the growth susceptor housing the crucible in order to prevent scattering of the Group V element by dissociation during melting and seeding of the raw material. The Group V element is heated such that its vapor pressure is higher than its dissociation pressure. As a result, fluctuation in the melt composition is also prevented. The vertical temperature gradient required for crystal growth is obtained by a combination of a heater and a heat-insulating material. When the power supplied to the heater is gradually decreased as the crystal grows, the crucible is cooled from its lower portion.
In order to grow a high-quality single crystal having a small number of crystal defects, not only the vertical temperature distribution but also horizontal (radial) temperature distribution must be considered. More specifically, assuming a certain horizontal plane of the crucible, when the temperature distribution is such that the compound semiconductor melt is solidified from the peripheral wall to the center of the crucible (when the temperature of the central portion of the crucible is higher than its remaining portion), a polycrystal tends to be formed. Therefore, it is preferable that the temperature distribution in the radial direction of the crucible is uniform or the temperature is low at the central portion and is higher toward the peripheral portion.
However, in the conventional method, the crucible is heated only from outside with a heater. Together with the influence of the melt convection, it is difficult to control the temperature distribution in the radial direction to be substantially uniform or the temperature to be low at the central portion.